Orosomucoid is a well studied serum glycoprotein. Its amino acid sequence is known and it possesses a single steroid receptor site with highest affinity for progesterone. It undergoes thermal polymerisation in a reversible manner, and also binds certain therapeutic drugs. The physiological function of orosomucoid is unclear, but it appears to have a role in lipid clearance. Also, orosomucoid may be a steroid receptor protein normally found in T and B cell membranes which is released following proteolytic scission. This research project is studying in detail the chemical nature and topography of the progesterone binding site, and the thermodynamic aspect of the binding process. These are to be related to the self associative properties of orosomucoid, and the sialic acid content of the molecule.